net: atlantic: move FRAC_PER_NS to aq_hw.h

This patch moves FRAC_PER_NS to aq_hw.h so that it can be used in both
hw_atl (A1) and hw_atl2 (A2) in the future.

Signed-off-by: Mark Starovoytov <mstarovoitov@marvell.com>
Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>